This is McCalls 4118. It was pretty easy, but I will make a few changes if I do another. For one, I will eliminate the strange zipper in the back. What is the point of that? Second, I will not quilt the inside and lining together, I will line the bag separately to avoid having to fight with bias tape.

I love the drawstring top on the bag. Usually those zippers on the back are meant so that if you are carrying the backpack over one shoulder you can access the contents easier than taking off the whole thing and opening the flap, undoing the drawstring, etc.